Refining mineral oils



Sept. 22, 1942. G; s. BAYs, JR., Erm.

REFINING MINERAL OILS Filed Dec. 9,'-1939 2 Sheets-Sheet 1 H NNQISU Sept 22, W42 G. s. BAYs, JR., ETAL REFINING MINERAL OILS Filed De- 9. 1939 2 Sheets-Sheet 2 LIQUID ET" Patented Sept. 22, 1.942

George S. Bays, Jr.,

Baytown,

and Joe L.

Franklin, Jr., Goose Creek, Tex., assignors to Standard Oil Development Company, a corporation of Delaware Application December 9, 1939, Serial No. 308,356

(Cl. 19d-18) 1 Claim.

The present invention relates to the refining of mineral oils. Thel invention is4 more particularly directed to the removal of waxy constituents from wax-bearing oils and especially relates` toY an efficient and economical method of cooling waxy oils invr order to precipitate the waxy con'- stituents. In accordance with the present process, the waxy oil is mixed' with a suitable sol-` vent and the mixture then chilled in stages by passing the same through a series of chilling vessels maintainedA at successively lower pressures and temperatures. In these chil-ling Vessels the waxy mixture is chilled' by evaporation of the solvent, which is not removedA from the respective vessels as vapor but is condensed on exchangerA tubes located in the vapor spaces of the respective vessels. The condensed solvent flows back into the waxy solution and' may be revaporized in order to further chill' additional' fresh waxy feed to the chilling stage in question. Complete chilling of the waxy mixture is preferably accomplished by evaporationof the solvent in a nal chilling vessel or vessels` of the series; The vapors from the final chilling vessel or ves= sels are notfcondensed Within the vessel itself buty are removedl and passed to compressors or other recovery means.

The removal of waxy constituentsfromv mineral oils containing the same by various methodsY is well known in the art. One method is to add a suitable diluent to the waxy oil or to take a wide distillate cut containing relatively loWer boiling hydrocarbons, which function as a diluent, and then to chill the mixture by external means to a temperature below the wax crystallization temperature. The precipitated' wax is separated from the dewaxed oil by any suitable means; such as by filtering, sedimentation, centrifuging, and the like. Another method is to employ a solvent or solvent mixture which tends to preferentially dissolve `the oily to the exclusion of the waxy constituents or which tends to facilitate precipitation of the waxy constituents. For example, it is known to employ substances of the class of liquefied normally gaseous hydrocarbons, such as propane, which material serves to act as a diluent and as a refrigerant. When propane or an equivalent agent is employed in a dewaxing operation, the process is usually carried out by adding the solvent to the waxy oil and allowing part of the solvent to evaporate throughout the body of the solution. The waxy oil-solvent mixture is chilled in this manner to a temperature at Which the waxy constituents are precipithe dewaxed oil by filtration or other means; The vaporized refrigerant is' removed from the chilling stage, usually compressed and condensed by means ofv cooling' water andthe like, and then recycled to the' system'. This method of chilling the waxy distillate presents' problemsA in' thev conservation of refrigeration. It is desirable that a minimum amount of propane'be vaporized to' cool the oil a desired' degreein order toV reduce the necessary compressor capacity and the like.

We have now discovere'da' process which willI permit a more economical' and eiii'ci'ent dewaxing operation by recovery of refrigeration' in an optimum manner. In accordance'with our invention',

' the waxy oil-solvent mixture' is'passed through a sels of the series by evaporation' of the solvent,

tated so that they may be readily separate'dfro'm 55` which Vaporized solvent is not withdrawn from the vessel in question but condenses on exchanger tubesv maintained' in the vapor space of the respective chillingV Vessel. The condensed' solvent flows back' into thewaxy oil solvent mixture and may be rev'apo'rized to secure futher chilling. A preferred modieation of the present inventiony is to' condense the vaporsV byv absorbing' heat therefrom by passing the chilled dewaxed oil solution through the condensing' tubes maintained in' the vapor spaces of the respective chillers. Complete chilling of the waxy oil i's accomplished in a nal Chiller or chillers by evaporation of additional solvent which is removed from the vessel and condensed by compression or othermeans.

The process of our invention' may be readily understood by reference to the attached' drawings illustrating modications of the same'. For purposes of description, it is assumed that the' feed oil is a waxy petroleum oily boiling in the lubricating oilrange and that the diluent is a liquefied normally gaseoushydrocarbon such asv propane.

Referring specifically to Figure l, the waxy -distillate is introduced into the chilling system by means of feed line I. The waxyA distillate is mixed with liquefiedV propane which is introduced into line I by means of line 2. The mixture is heated in heater 3 to a temperaturesubstantially above that at which complete miscibility occurs between the respective constituents. The heated mixture is introduced into cooler 4 by means of line 5, and then passed into an initial cooling stage 6 by means of line The'mixture in Chiller 6 is cooled by vaporization of propane. The vaporized propane passes upwardly in unit 6` and is condensed by contacting condensing tubes 23 maintained in the vapor space of chiller 6. The condensed propane then ilows back into the liquid solution and may be again revaporized in order to eiect further cooling. The chilled mixture is withdrawn from chiller 6 by means of line 8 and introduced into secondary chiller 9.

' 'I'he mixture is further Ycooled in chiller 9 by further vaporization of propane. The vaporized propane in chiller 9 passes upwardly and is condensed by contacting condensing tubes 24 maintained in the vapor space of chiller 9. 'Ihe condensed propane ows back into the oil and may be revaporized in order to secure further chilling. In a similar manner the partially chilled waxy oil is passed to chillers I0, I2, and I3 by means of lines II, I4, and |5 respectively. The oil is further cooled in these chillers by vaporization of propane, which vaporized propane is not removed from the Chillers, but is condensed by contact with condensing, tubes 25, 26, and 21 maintained in the vapo-r spaces of chillers II), I2, and I3 respectively. The chilled distillate is withdrawn from chilling unit I3 by means of line I1 and introduced into a nal chilling unit I6 in which complete chilling of the oil is secured by Vaporizing an additional quantity of propane which is removed overhead from chiller I6 by means of line I8. This propane is passed to compressor 21, condenser 28, and then to propane storage 29. The completely chilled oil is withdrawn from unit I6 by means of line 20 and introduced into filters or other equivalent means I9 in which the precipitated waxy constituents are separated from the dewaxed oil. The waxy constituents are removed from lters I9 by means of line 2| and handled in a manner to remove `the final traces of propane and further refined,

if desired, to produce rened waxes and the like. The cold dewaxed oil is withdawn from lters I9 by means of line 22 and then passed successively through condensing tubes 21, 26, 25, 24, and 23 maintained in the Vapor spaces of chilling units I3, I2, I0, 9, and 6 respectively. The

warmed oil is withdrawn from condenser tubes 23 by means of line 3|) and treated in a manner to remove the propane. This is preferably accomplished by passing the dewaxed oil to desolventizer 3|, wherein the propane is completely separated from the dewaxed oil. The propane is removed overhead from depropanizer 3| by means of line 32, passed to compressor 33, con- -denser 34, and then returned topropane storage 29 by means of line 35. The dewaxed oil completely free of propane is withdrawn from desolventizing unit 3| by means of line 4| and handled in any manner desirable. Under certain circumstances it may be desirable, in order to control the temperature within the respective chillers, to by-pass a certain amount of the cold dewaxed oil around one or more chillers. This may -be readily accomplished by passing the dewaxed oil to solvent recovery unit 3| by means of lines 36, 31, 38, 39, and 40. i

Figure 2 illustrates another modication of the present invention. Waxy feed oil is introduced into the system by means of line 50, mixed with propane which is introduced by means of line 5|, passed through heating unit 52, cooler 53, and then introduced into tower 54 by means of line 55. Tower 54 comprises three kchilling stages 56, 51, and 58. The mixture of propane and waxy oil is introduced into stage 56 maintained in the upper part of tower 54. The waxy oil is chilled in stage 56 by vaporizing propane. This propane passes upwardly in stage 56 through bubble cap plate or equivalent means 59 and is condensed on condenser tubes 60 maintained in the vapor space of stage 56. The condensed propane flows on to bubble cap plate 59 and then back into the waxy oil, wherein it is revaporized in order to secure further chilling of the waxy oil. The pai'- tially chilled waxy oil is withdrawn from stage 56 by means of line 6| and introduced into the lower section of stage 51. The liquid level of the waxy oil in stage 56 and the rate at which the partially chilled oil is introduced into stage 51 are controlled by a iloat control valve arrangement 62. In stage 51 the waxy oil is further chilled by vaporization of propane which passes upwardly through bubble cap plate 63 and is condensed on condenser tubes 64 maintained in the vapor space of stage 51. The vaporized propane condensed on tubes 64 ows on to bubble cap plate 63 and then into the waxy oil, wherein it may be revaporized to effect further cooling. In a similar manner the partially chilled oil is passed to chilling stages 58, 65, 66, and 61 by means of lines 68, 69, 10, and 1|. The liquid levels in stages 51, 58, 65, 66, and 61 are controlled by float control valve arrangements 12, 13, 14,15, and 16 respectively. The oil is chilled in stages 58, 65, and 66 by vaporizing propane, which vaporized propane is not removed from the stage, but is condensed on condenser tubes 11, 18, and 19 respectively. The condensed propane ows on to bubble cap plates 88, 8|, and 82 maintained in the respective stages and then back into the liquid from which it may be revaporized to secure additional cooling. The chilled oil is withdrawn from stage 66 and introduced into a chilling stage 61 maintained in the lower section of tower 83 by means of line 1|. Further chilling of the waxy distillate is secured by vaporizing propane in stage 61, which propane passes upwardly through bubble cap plate or equivalent means 84 and is withdrawn from stage 61 by means of line 85. The propane is passed through compressor |82 to condenser 86 and then returned to propane storage. Cold propane wash from the lters or from Vdirect exchange of storage propane with cold wax from the filters can be admitted above the bubble cap tray or other device 84 in Chiller 61 by means of line |65 if desired. The chilled waxy oil is withdrawn from stage 61 by means of line 81 and passed to unit 88, wherein the solvent-waxy distillate mixture is finally chilled. Vaporized propane is withdrawn from unit 88 by means of line 89, compressed in compressor 96, condensed in condenser 86 and then returned to propane storage. The waxy distillate-solvent mixture is withdrawn from unit 88 by means of line 9| and passed through lters or other equivalent means 92 in which the precipitated waxy constituents are separated from the dewaxed oil. The waxy constituents are removed from lters 92 by means of line 93 and passed through exchanger |83 to chill storage propane to be used for washing oil from wax in the filters and for direct addition to chilling stage 61 through line |05. The waxy constituents leaving exchanger |63 are handled in a manner to remove and recover the propane. The propane is condensed and returned to propane storage, while the'waxy constituents may be rened in any manner desirable. Wash propane introduced into the filters by means of line 94 is withdrawn through line |84 and added to chiller 88 and also to chiller 61 if desired. The

cold dewaxed oil is withdrawn from filters 92,k

by means of line 9;5,and passed .through Acondenser tubes 79, ,1.8, 1.7, .64, and *.60 maintained in the vapor space of chilling ,stages 166, 6.5, 153, 51, and 56 respectively. The warm dewaxed oil solution is Vwithdrawn from condenser tubes by means of line y96 and handled in amanner to remove the propane from the .dewaxed .oi-l.V The propane is condensed and returned to propane storage, while the dewaxed oil may 'be handled Ain .any manner desirable. In order to control the Operating conditions .o f any particular operating stage, the cold dewaxed oil maybe partially by-passed around condenser tubes 60, 64, TI, '18, and 19 by means of lines 91, 98, 99, |00, and ll respectively.

The process of the present invention may be widely varied. Although the waxy oil is preferably chilled in a series of more than two chilling stages, it is to be understood that a two-stage system may also be employed in which only one condensing stage is provided. The process may be applied in the removal of waxy constituents from any wax-containing oil. The particular refrigerant used likewise may be any suitable substance, as, for example, ethane, propane, butane, sulfur dioxide, and the like. Also, mixtures of a solvent and a refrigerant may be employed such as mixtures of propane and methyl normal-butyl ketone, sulfur dioxide and benzene, and the like. The invention, however, is particularly applicable when employing a liquefied normally gaseous hydrocarbon, especially liquefied propane.

The present invention constitutes an improvement in that the chilling is accomplished continuously, and in that efcient utilization of refrigeration is achieved. By operating in accordance with the present process, it is easily possible to charge waxy oil and propane to such a chilling system at 100 F. and to remove the dewaxed oilsolvent mixture and wax-solvent mixture from the system at 80 F. The heat required to warm the dewaxed oil solution is abstracted from the waxy oil-solvent charge by vaporizing and condensing propane in the manner described. Heat required to warm the ltered wax is abstracted from liquid propane which is added either before or after use as a filter wash to the final chillers to equal the amount of propane to be vaporized therefrom. Removal of the dewaxed oil-solvent mixture and the wax-solvent mixture from the dewaxing system at temperatures so closely approaching that of the waxy oil-solvent mixture charged to the chilling system represents a distinct advancement in conservation of refrigeration. Because of limitations inherent in dewaxing processes employing liquefied propane or an equivalent agent as the refrigerant, commercial dewaxing systems now in operation employing batch chilling systems discard the dewaxed oil-solvent mixture to solvent recovery units at temperatures of from 50 to 60 F. when charging a waxy oil-solvent mixture to the chilling system at temperatures in the range from about 90- 100 F. The improved refrigeration economy obtained by employing the present process is accomplished without the formation of waxy crystals on the exchanger tubes thus ensuring eiTlcient heat transfer at all times. The use 0f expensive scraped-surface type heat exchangers, as employed in some current dewaxing processes is not necessary.

In order to illustrate the process of the present invention, the following example is given which should not be construed as limiting the same in any manner whatsoever:

Example A waxy distillate secured'jfrom a Mid-Contig nent crude oil was mixed with .three volumesl of propane, `based upon the volume of waxy oil, and the mixture heated to a temperature of about 150 The heated mixture was .cooled to about F. vby heat exchange with cooling water and passed through a Vseries of five chillers maintained at successively lower temperatures yand pressures. These .ve chillers contained cohdensing coils in the vaporspaces of the same, upon which the propane vaporized in the respective chillers was condensed. The operating conditions of these chillers were controlled by regulating the amount of chilled dewaxed oil passed through the condensers located in the vapor spaces of the respective chillers. The waxy mixture leaving the last chiller containing therein a condensing coil was then passed through two additional chilling stages, from which vaporized propane was removed and passed to two compressors operating at successively lower suction pressures. The temperature and pressure conditions on the respective stages were as follows:

Temp. of oil leaving stage Pressure Chilling stage #1 (containing condensing F. LI1s./sq. in.

condensing co 72 115 Chilling stage #3 (containing condensing condensing 34 58 condensing -5 21 Chilling stage #6 (no condensing coil) -25 S Chilling stage #7 (no condensing coil) -50 The chilled waxy solution was passed through rotary filters at -50 F. and the wax separated.

The cold dewaxed oil solution was then passed through the condensers maintained in the vapor spaces of the respective chillers in accordance with the process of the present invention. Cold waxy constituents containing some solvent removed from the filters at -50 F. were used to cool liquid propane withdrawn from storage to about 25 F. A sufficient amount of this chilled propane was added to the 25 F. chiller to adjust the ratio of liquid propane to waxy oil in the solution leaving the final chiller at 50 F. equal to labout three volumes of propane to one volume of oil, lbased upon the respective volumes at 60 F. The remainder of this 25 F. propane was used as filter wash and discharged from the filters in` admixture with the dewaxed solution. When operating as described at a feed charge rate of 4,000 barrels per day and 12,000 .barrels per day of propane to the chilling system, it was possible to reduce the number of compressors yby three and to effect other material savings over other conventional chilling methods in investment and operating cost.

The process of the present invention is not to be limited by any theory or mode of operation, but only in and by the following claim in which it is desired to claim al1 novelty insofar as the prior art permits.

We claim:

A process for dewaxing mineral oils which comprises passing a waxy mineral oil containing .propane in solution through a plurality of successive cooling zones, chilling the oil in each zone by vaporization of at least a portion of the propane therein, condensing the vaporized propane in each respective zone by indirectly contacting it with cooling coils in the vapor space of each zone, collecting the condensed propane on a bubble cap plate in each cooling zone below said cooling coils but above the liquid level in each cooling zone before returning it to each respective cooling zone, withdrawing the cooled oil from the bottom of each zone and passing it to the next zone, further cooling the oil in a nal zone by .direct contact with added liquefied propane and without using a cooling coil, ltering the cooled oil leaving `the last zone to remove precipitated Ivmxy constituents therefrom, passing the cold filtered oil through said cooling coils countercurrent to the flow of the oil being deWaxed, adding propane to Wash oil from the waxy constituents in the filtering step, precooling the wash propane by contacting it indirectly with the cold waxy :constituents leaving the filtering step and adding at least a portion of the precooled wash propane to the last oil .chilling zone :for direct contact with 10 the' oil and to further cool the oil.

GEORGE S. BAYS, JR. JOE L. FRANKLIN, JR. 

